Use of halophytic plants for recycling NaCl in human liquid waste in a bioregenerative life support system

The purpose of this work was to develop technology for recycling NaCl containing in human liquid waste as intrasystem matter in a bioregenerative life support system (BLSS). The circulation of Na+ and Cl− excreted in urine is achieved by inclusion of halophytes, i.e. plants that naturally inhabit salt-rich soils and accumulate NaCl in their organs. A model of Na+ and Cl− recycling in a BLSS was designed, based on the NaCl turnover in the human-urine-nutrient solution-halophytic plant-human cycle. The study consisted of (i) selecting a halophyte suitable for inclusion in a BLSS, and (ii) determining growth conditions supporting maximal Na+ and Cl− accumulation in the shoots of the halophyte growing in a nutrient solution simulating mineralized urine. For the selected halophytic plant, Salicornia europaea, growth rate under optimal conditions, biomass production and quantities of Na+ and Cl− absorbed were determined. Characteristics of a plant production conveyor consisting of S. europaea at various ages, and allowing continuity of Na+ and Cl− turnover, were estimated. It was shown that closure of the NaCl cycle in a BLSS can be attained if the daily ration of fresh Salicornia biomass for a BLSS inhabitant is approximately 360 g.